1. Field of the Invention
The present invention relates to a Metal Oxide Semiconductor (MOS) type semiconductor device, particularly to its junction structure between source/drain diffusion layers and metallic interconnections.
2. Description of the Prior Art
A representative example of this type of semiconductor device of a prior art is shown in FIG. 1(a) by way of a plan view and in FIG. 1(b) by way of a cross section along the line A--A' shown in FIG. 1(a).
In these drawings of FIGS. 1(a) and 1(b), 1 denotes a silicon substrate, 2 denotes a field oxide film, 3 denotes a gate oxide film, 4 denotes a gate electrode, 5 denotes a low concentration diffusion layer, 6 denotes a side wall oxide film, 7 denotes a high concentration diffusion layer, 8 denotes a first layer insulation film, 11 denotes an aluminum interconnection and 14 denotes a contact hole.
Up to the present, electric connection between a diffusion layer region and an aluminum interconnection, particularly in a transistor having a large width of a diffusion layer (length in a channel width direction), has been made by opening a contact hole 14 on a diffusion layer near a gate electrode 4 in a direction along which the gate electrode extends and patterning an aluminum interconnection 11 to cover the contact hole 14 thereby, as shown in FIGS. 1(a) and 1(b), in order to suppress decrease of ON current of the transistor owing to resistance of the diffusion layer.
In a semiconductor integrated circuit having logic gates, ratio of an area occupied by aluminum interconnections to an area of the entire chip is very large, particularly when compared with that of a memory series semiconductor integrated circuit. Therefore, it is a significant subject for enhancing integration degree, how the aluminum interconnections are disposed in an efficient manner. In a transistor of prior art structure, when it has a large width of a diffusion layer, aluminum interconnections for connection to the diffusion layer are disposed to surround a gate electrode in a channel portion, and so it is impossible to dispose other aluminum interconnections in this portion of the transistor, hence efficient disposition of aluminum interconnections has been obstructed.